First things first, you don't need to bother editing rosters, changing sliders or even changing the teams. Go into whichever tournament you need the win for, and on the screen where you pick the teams, just press X next to each team to play as every team. Simulate up to the final game, and 2 of your teams will be playing each other. Play this final game with 2 controllers to ensure you win it, time can be set to 2-minute halves.
This method works with all tournaments.